Structure of YM-254890, a Novel Gq/11 Inhibitor from Chromobacterium sp. QS3666

The isolation and structure elucidation of YM-254890, a novel G_q/11 inhibitor from Chromobacterium sp. QS3666, is described. The gross structure was determined by one- and two-dimensional NMR studies and mass spectrometry. YM-254890 is a cyclic depsipeptide containing uncommon amino acids; β-hydroxyleucine (two residues), N,O-dimethylthreonine and N-methyldehydroalanine. YM-254890 exists as a mixture of two conformers in a variety of NMR solvents, and the distinction between major and minor conformers appears to lie in the geometry of the amide bond between 3-phenyllactic acid and N-methyldehydroalanine. The absolute stereochemistery was elucidated by Marfey's analysis and chiral HPLC analysis of the acid hydrolysate of YM-254890.     

Total synthesis of (+)-macquarimicin A

The first total synthesis of (+)-macquarimicin A (1), a novel inhibitor of neutral sphingomyelinase (N-SMase) with antiinflammatory activity, has been accomplished. The present work determined the absolute configuration of (+)-1 and revised the C(2)-C(3) geometry to be Z. The synthesis features a transannular Diels-Alder reaction, which constructed the tetracyclic framework stereoselectively, and a convergent and efficient synthetic pathway, which afforded (+)-macquarimicin A (1) in 27 steps (longest linear sequence) with 9.9% overall yield.     

Development of hydrophilic fluorogenic derivatization reagents for thiols: 4-(N-acetylaminosulfonyl)-7-fluoro-2,1,3-benzoxadiazole and 4-(N-trichloroacetylaminosulfonyl)-7-fluoro-2,1,3-benzoxadiazole

Sensitive, reactive, and hydrophilic fluorogenic reagents for thiols with the benzofurazan skeleton, 4-(N-acetylaminosulfonyl)-7-fluoro-2,1,3-benzoxadiazole (AcABD-F) and 4-(N-trichloroacetylaminosulfonyl)-7-fluoro-2,1,3-benzoxadiazole (TCAcABD-F) have been developed. These reagents reacted with thiols within 10 min at 60 degrees C. AcABD-F and TCAcABD-F themselves do not fluoresce but are strongly fluorescent after the reaction with thiol compounds. The generated derivatives were highly water-soluble, since they dissociated a proton and ionized in the neutral pH region. The derivatives with four biologically important thiol compounds were separated on a reversed-phase HPLC column and detected fluorometrically at 504 nm with excitation at 388 nm. The detection limit attained for homocysteine with AcABD-F was 25 fmol on column (11 nM) (signal-to-noise ratio = 3), and that for glutathione with TCAcABD-F was 45 fmol on column (20 nM).     

Linear NiII-MnIII2-NiII tetramers: an oligomeric component of the MnIII2NiII single-chain magnets

Heterometallic linear tetramers [Mn(5-R-saltmen)Ni(pao)(bpy)(2)](2)(ClO(4))(4) (5-R-saltmen(2-) = N,N'-1,1,2,2-tetramethylethylene bis(5-R-salicylideneiminate); pao(-) = pyridine-2-aldoximate; bpy = 2,2'-bipyridine, R = H, 1; Cl, 2; Br, 3; MeO, 4) have been synthesized and structurally characterized. These compounds exhibit a [Ni(II)-NO-Mn(III)-(O)(2)-Mn(III)-ON-Ni(II)] skeleton where -ON- is an oximate bridge between Mn(III) and Ni(II) ions and -(O)(2)- is a bi-phenolate bridge between Mn(III) ions. These tetramers can be seen as oligomeric units of the heterometallic Mn(III)(2)-Ni(II) chain observed in a family of single-chain magnets (Clérac, R.; Miyasaka, H.; Yamashita, M.; Coulon, C. J. Am. Chem. Soc. 2002, 124, 12837. Miyasaka, H.; Clérac, R.; Mizushima, K.; Sugiura, K.; Yamashita, M.; Wernsdorfer, W.; Coulon, C. Inorg. Chem. 2003, 42, 8203.). Magnetic measurements on these tetramers confirm the nature of the magnetic interactions reported for the Mn(III)(2)-Ni(II) chains: a strong antiferromagnetic Mn(III)/Ni(II) coupling via the oximate bridge (J(Ni-Mn) ranges from -23.7 to -26.1 K) and a weak ferromagnetic Mn(III)/Mn(III) coupling through the bi-phenolate bridge (J(Mn-Mn) ranges from +0.4 to +0.9 K). These magnetic interactions lead to tetramers with an S = 2 ground state.     

MnIII2 (5-Rsaltmen)2NiII(pao)2(L)]2+: an S(T)=3 building block for a single-chain magnet that behaves as a single-molecule magnet

Mn(III)-Ni(II)-Mn(III) linear-type trinuclear complexes bridged by oximate groups were selectively synthesized by the assembly reaction of [Mn2(5-Rsaltmen)2(H2O)2](ClO4)2 (5-Rsaltmen2-=N,N'-(1,1,2,2-tetramethylethylene) bis(5-R-salicylideneiminate); R=Cl, Br) with [Ni(pao)2(phen)] (pao-=pyridine-2-aldoximate; phen=1,10-phenanthroline) in methanol/water: [Mn2(5-Rsaltmen)2Ni(pao)2(phen)](ClO4)2 (R=Cl, 1; R=Br, 2). Structural analysis revealed that the [Mn(III)-ON-Ni(II)-NO-Mn(III)] skeleton of these trimers is in every respect similar to the repeating unit found in the previously reported series of 1D materials [Mn2(saltmen)2Ni(pao)2(L1)2](A)(2) (L(1)=pyridine, 4-picoline, 4-tert-butylpyridine, N-methylimidazole; A=ClO4-, BF4-, PF6-, ReO4-). Recently, these 1D compounds have attracted a great deal of attention for their magnetic properties, since they exhibit slow relaxation of the magnetization (also called single-chain magnet (SCM) behavior). This unique magnetic behavior was explained in the framework of Glauber's theory, generalized for chains of ferromagnetically coupled anisotropic spins. Thus, in these 1D compounds, the [Mn(III)-ON-Ni(II)-NO-Mn(III)] unit was considered as an S(T)=3 anisotropic spin. Direct-current magnetic measurements on 1 and 2 confirm their S(T)=3 ground state and strong uniaxial anisotropy (D/k(B) approximately -2.4 K), in excellent agreement with the magnetic characteristic deduced in the study on the SCM series. The ac magnetic susceptibility of these trimers is strongly frequency-dependent and characteristic of single-molecule magnet (SMM) behavior. The relaxation time tau shows a thermally activated (Arrhenius) behavior with tau0 approximately 1x10(-7) s and Delta(eff)/k(B) approximately 18 K. The effective energy barrier for reversal of the magnetization Delta(eff) is consistent with the theoretical value (21 K) estimated from |D| S2T. The present results reinforce consistently the interpretation of the SCM behavior observed in the [Mn2(saltmen)2Ni(pao)2(L1)2](A)2 series and opens new perspectives to design single-chain magnets.     

Practical synthesis of a neuropeptide Y antagonist via stereoselective addition to a ketene

[Reaction: see text]. The synthesis of neuropeptide Y antagonist 1, currently under clinical investigation for the treatment of obesity, is described. The convergent synthesis from trans-spirolactone carboxylic acid intermediate 2a and aminopyrazole 3 is predicated on a stereoselective route to the former. The coupling reaction of ethyl 4-oxocyclohexanecarboxylate (10a) with lithiated isonicotinamide 11 was investigated in detail, but even optimized conditions only provided a 45:55 ratio of trans:cis isomers (12a:12b). While selective crystallization schemes were developed to isolate the thermodynamically less stable trans isomer 2a, improved stereocontrol was subsequentially achieved by the application of ketene chemistry. The ketene formation and quench was investigated under a variety of conditions aimed at maximizing the trans:cis ratio. Reacting a mixture of carboxylic acids 2a and 2b with POCl3 in THF, followed by concomitant addition of tert-butyl alcohol in the presence of TMEDA at 35 degrees C provided a 4:1 ratio of trans:cis tert-butyl esters (18a:18b) via in situ ketene formation. Ester hydrolysis, followed by selective crystallization of undesired 2b as the HCl salt, led to isolation of 2a in 47% overall yield. Aminopyrazole intermediate 3 was synthesized via the condensation reaction of 2-fluorophenylhydrazine hydrochloride (4a) with acrylonitrile derivative 5 in 65-70% yield. Coupling of advanced intermediates 2a and 3b via activation with thionyl chloride gave a 92% yield of 1.     

Synthesis of the common left-half part of pectenotoxins

The common left-half [C31-C33(OC1-C7)-C40] part of pectenotoxins has been synthesized convergently from the C31-C35, C36-C40, and C1-C7 parts. The C31-C35 part, prepared via a new route shorter than our previous route, was coupled with the C36-C40 part through reductive lithiation and addition reactions to give an adduct stereoselectively, which was converted to a cyclic acetal corresponding to the C31-C40 part. The left-half was synthesized by a three-step process including esterification of the C31-C40 part with the C1-C7 part.     

Structure and magnetic properties of the two-dimensional ferrimagnet (NEt4)[[Mn(salen)]2Fe(CN)6]: investigation of magnetic anisotropy on a single crystal

The title compound, (NEt(4))[[Mn(salen)](2)Fe(CN)(6)] (1), was synthesized via a 1:1 reaction of [Mn(salen)(H(2)O)]ClO(4) with (NEt(4))(3)[Fe(CN)(6)] in a methanol/ethanol medium (NEt(4)(+) = tetraethylammonium cation, salen(2)(-) = N,N'-ethylenebis(salicylidene)iminate). The two-dimensional layered structure of 1 was revealed by X-ray crystallographic analysis: 1 crystallizes in monoclinic space group P2(1)/c with cell dimensions of a = 12.3660(8) A, b = 15.311(1) A, c = 12.918(1) A, beta = 110.971(4) degrees, Z = 2 and is isostructural to the previously synthesized compound, (NEt(4))[[Mn(5-Clsalen)](2)Fe(CN)(6)] (5-Clsalen(2-) = N,N'-ethylenebis(5-chlorosalicylidene)iminate; Miyasaka, H.; Matsumoto, N.; Re, N.; Gallo, E.; Floriani, C. Inorg. Chem. 1997, 36, 670). The Mn ion is surrounded by an equatorial salen quadridentate ligand and two axial nitrogen atoms from the [Fe(CN)(6)](3-) unit, the four Fe[bond]CN groups of which coordinate to the Mn ions of [Mn(salen)](+) units, forming a two-dimensional network having [[bond]Mn[bond]NC[bond]Fe[bond]CN[bond]](4) cyclic repeating units. The network is spread over the bc-plane of the unit cell, and the layers are stacked along the a-axis. The countercation NEt(4)(+) is located between the layers. Compound 1 is a ferrimagnet with T(c) = 7.7 K and exhibits hysteresis with a remnant magnetization of 13.44 cm(3).mol(-1) (M/N mu(B) = 2.4) at zero field and a coercivity of 1000 Oe when the powder sample was measured at 1.9 K. Magnetic measurements of a direction-arranged single crystal were also carried out. The orientation of the crystallographic axes of a selected single crystal was determined by X-ray analysis, and magnetization was measured when an external field was applied in the a*, b, and c directions. The magnetization in the a* direction increased more easily than those in the b and c directions below the critical temperature. No hysteresis was observed only for the measurement in the a* direction, indicating the presence of strong structural anisotropy with potential anisotropy on Mn(III) ions.     

Effects of beta-sheet breaker peptide polymers on scrapie-infected mouse neuroblastoma cells and their affinities to prion protein fragment PrP(81-145)

The effects of Soto's 'beta-sheet breaker peptide' and its polymer on PrPSc formation in ScN2a cells were investigated. Surface plasmon resonance study indicated that direct binding between PrP(81-145) and the 'beta-sheet breaker peptide' is not specific and may not play a major role in the inhibition of PrPSc formation.     

Mapping analyses of Fe-diffused mc-Si using M?ssbauer microscope and photoluminescence

Twenty CK chondrites collected in the Antarctica Continent were characterized by inductively-coupled plasma mass spectrometry (ICP-MS), prompt gamma ray analysis (PGA), instrumental neutron activation analysis (INAA), X-ray diffractometry (XRD) and ⁵⁷Fe-M?ssbauer spectroscopy. As a result of elemental analysis, it was revealed that 18.2~26.4 mass% of iron was included in the each chondrite. M?ssbauer spectrum of LEW86258, classified as a typical CK chondrite, was found to be composed of two paramagnetic doublets and two magnetic sextets. M?ssbauer spectra were assigned to the absorption due to forsterite (Mg_1.36Fe_0.64SiO₄) and magnetite (Fe₃O₄), as also confirmed by XRD. XRD study of LAP03834, reclassified from CK to R chondrite, revealed the presence of crystalline phase due to forsterite. These results indicate that LAP03834 and related chondrites, i.e., MET01149, LAP03923 and MAC02453, should be reclassified as R or LL chondrite.